UnderRealmSetting

I should note that this section partly reveals the inspiration and physical science of what i believe the caverns are the result of. This knowledge in many places breaks the fourth wall, it is knowledge people in the UnderRealm would in several cases, not have. They do not understand what a antibiotic is, only that goop can cure fevers and chills. In many places, liberties are taken with the science but it's broadly based on my background in geophysical science and geology.

Geology

The UnderRealm is a series of caverns, tunnels that stretches for untold thousands of kilometers. Caverns vary considerably in size, the middle and most common size is about several kilometers in diameter, some can be considerably larger, whilst underhold caverns tend to be smaller expect for the main city chambers.

Temperatures vary, the uppermost reaches of the Upper realms can reach low enough to freeze water, whilst the deeper lower realms can reach upwards of 30C. The main caverns of a Underhold are nearly always 21C, presumely due to unknown mechanisms of climate control.

Many caverns are formed in limestone, but other rock types include chalk, dolomite, marble and salt. These are formed from slightly acidic fluid flows that slowly weather the rock.

The second most common form of cavern and one that dominates in many areas, are lava caves. These are the result of long-drained lava flows and form tunnels and large caves with relatively smoother walls than that seen in solutional limestone caverns. The rock of these caverns in primarily granite, Gabbro and other itrusive igneous rocks.

A surprisingly common type of cavern is artificial, having being clearly cut from the native rock. Whilst the most famous of these are underholds, there are plenty of caverns that appear natural at first, but have clearly artificial origins if given closer scrutiny. Many of these caverns appear to be particularly suited to growing goop, fungi and mushrooms.

In addition, the most recent arrivals to the underrealm often fashion their own caverns and tunnels, digging, filling and fortifying.

Areas of Special Interest

Sunstone Lake

Several veins of sunstone stretch across the bed of this vast lake. Several hundred kilometers from shore to shore, it forms the largest known cavern in the under-realm. One major underroad crosses the span of the lake, linking several nearby Underholds together. The lake is rich in wildlife and photosynthetic plants. It is believed much of the freshwater in the Underhold system is derived from this watersource.

The Deep Veins

An area known for it's deposits of metals including nodules of rare mythic metals, thick veins of ores stretch deep throughout the region. The mines here have endured for centuries without ceasing to find more ore. Some mines are so labyrinth, castles have been built within to shelter and house the workers that dig ever wider and ever deeper.

The Geode Pits

An area which contains several large nodules of adamantium and other mythic ores, which are found in meter long geodes, often located within pit like cavities within the rock.

UnderHolds

Underholds take many forms, at the most basic, they contain a central large chamber, enclosed entirely by the dark hexongal panelling on the walls roof and floors, covered with granite or marble blocks. The chambers can be many shapes, from cylinders hundred of meters wide and several kilometers tall, to wide and low chambers more like a traditional city.

Some Underholds resemble giant castles, endless corridors and rooms, while others are like a city in a giant chamber, full of buildings and streets. Some are a mixture of both. Sunstone is commonly inset into walls and ceilings, provide light.

Most underholds have little understood sanitation systems, which

Flora and Fauna

Flora

Goop

The most basic form of life in the caverns is bacteria. Known as goop, the bacteria feeds on thousands of tiny fissures that leak warm mineral rich water located in many caverns of all types. It forms a thick biofilm of slime about 20 centimeters in thickness on average. The dominant form of bacteria is perfectly harmless to humanoids and its strong antibiotic action has effectively eliminated the competition in the caverns it is found. Goop is bio-luminescent and generally a light blue in color.

Goop is also the staple food source for humanoids, the top layer can be easily scrapped off every few weeks and mixed with basic plants to create a fairly palatable porridge.

Plants

Without access to sunlight, plants relies on the bacteria in order to fuel their cells. Plantlife has a symbotic relationship with the goop, helping to stabilize the biofilm and draw up water. Whilst having no leaves, they still have branches and stalks, often ending in fruity bulbs of organic matter.

Plants of note include but are not limited to..

Infriti

Infriti plants have bulby fruits that are filled with thick oil that burns slowly without smoke, producing a orange light. Used in fireplaces and lanterns throughout, and also for more nefarious purposes, it will gladly stick to skin and burn through to bone. Many consider this a relatively abhorrent use.

Iron Stalk

Iron Stalks are similiar to trees, they provide a dark tough wood that is difficult to burn.

Quiet Vines

A thankfully rare carnivorous plant, it's true form is little known, but it is named after the vines that emit a short lived noxious humour to paralyse prey. Thankfully most suffocate before being devoured.

Surface plants

Fauna

The animals of the underrealm are varied, from the relative innocuous cave mouse, to the venomous giant spiders and the creepy octopus. The following are but a small but flavorful selection.

Lesser Wyrm

A popular creature is the now household companion, the lesser Wyvern. The size of a dog, these leathery creatures have been described as lizard-like bats and have a similar appearence to mythic tales of 'dragons'. They often ::roost upsidedown in caverns and have a diet that includes giant spiders. Tamed for hundreds of years, many breeds exist from the cute and feathery, to the ferocious and loyal War Wyverns popular with soldiers.

Wyrm

A rarer more expensive breed of Wyrm. The size of a horse, these leathery creatures have been described as lizard-like bats and have a similar appearence to mythic tales of 'dragons'. They often ::roost upsidedown in caverns and have a diet that includes giant spiders. These are typically used as mounts by cavalry, as horses are ill-suited to areas outside of cities.

Octopod

The Octopod is a bizzare creature with strong muscular tentacles and a bulbous head with a rubbery soft skull. They have suckers which attach well to cavern walls and two tentacles in particular have sharp claws suited to digging. These are typically to build predatory hideouts from which they can lurk, waiting for unsuspecting prey. While a soldier in plate is relatively safe at first, octopods are devilishly intelligent and can pry the armor off if given the chance.

Giant Spider

Probably the most famous denizen of the under-realm, the giant spider is on the whole rather timid. Relatively intelligent they will only pounce on anything caught in their webs, something only wyvernfire or the repeated heft of a sharp blade can free you from. Giant spiders have been bred for some time, and many species are quite tame and defanged. They are kept for the strong 'steelsilk' (not actually as strong as steel) they weave, which can be used for crossbow strings.